A recent study looked at 2300 women over 55 years old and found that if their vitamin D serum level were greater than or equal to 40 ng/ml, then they had a 67% lower risk of cancer than those with serum levels <20 ng/ml (P-value = .02). Read paper.

The standard recommendation levels of vit D level is 40-60 ng/ml.

So, why should we test, rather than just take vitamin D supplements daily?

The same people who did this study also found that when measuring vitamin D blood serum levels, supplementation response varies greatly person-to-person. For example, 2 people could both take 4,000 IU/day, they both measure their vitamin D levels and one could have the level 10 ng/ml, while another could be 120 ng/ml – a 10-fold variation in response to the same supplementation dose of 4,000 IU/day.

Reasons for such variability can be due to skin tone (those with darker skin tones need to spend more time in ultraviolet light to make vitamin D than those with lighter skin tones), gut absorption, and utilizations in the body.

So rather than just supplement your vitamin D, check your serum level with your doctor. It’s called Serum 25-Hydroxyvitamin D. Read more about Vitamin D here.